1. Field of the Invention
The present invention is directed to apparatus and methods for measuring the diameter and ovality of tubulars e.g., but not limited to, pipe, tubing, risers, and casing. In certain particular aspects, this invention relates to techniques and systems for detecting irregularities in either the diameter (inner and/or outer) or the ovality of oilfield tubulars by non-destructive testing equipment.
2. Description of Related Art
The prior art reveals a variety of non-destructive testing equipment to measure ovality of tubulars and to detect material defects in them. Ultrasonic and electromagnetic testing techniques and equipment can detect material defects at rates in the range of from 40 to 400 thirty-foot joints of pipe per hour. Relatively high speed testing equipment reduces the cost of non-destructive testing and reduces the lead time between a pipe order to an inspection yard and the delivery of inspected oilfield tubulars to a well site. Prior art equipment has been used for detecting irregularities in the outside diameter and ovality of oilfield tubulars; but many oilfield tubulars are still manually checked with O.D. calipers. While manual checking operations may be satisfactory when only random checks are to be made on a lot of oilfield tubulars, this technique can become too expensive and time consuming when numerous axial locations along the length of a tubular are to be checked for outer diameter and ovality conformance. In some cases manual checking of oilfield tubular diameter and ovality is not practical.
In one prior art testing system, a pair of light beams are each directed traverse to the axis of the tubular. A pair of relatively wide light beams strike radially opposing sides of the tubular, so that the tubular material blocks light to alter the width of each beam. The spacing between the reduced width beams is accordingly a measure of the diameter of the oilfield tubular. Optical systems can test oilfield tubular diameters at a rate commensurate with the speed of non-destructive equipment systems used for testing oilfield tubulars.
With certain prior art systems some problems remain; e.g. with some existing optical testing systems a relatively long time period is required to process data from detectors which sense the presence of light and generate raw data indicative of the spacing between the reduced width light beams. In may cases orders to inspection yards are typically performed on a first-in/first-out basis; successive orders are rarely for the same pipe size, and a single inspection order may require the testing of different oilfield tubular sizes. One or more recalibrations of the testing equipment may be needed. In some cases a test standard corresponding to a specific size tubular to be tested is positioned within testing equipment and the equipment is then calibrated or “zeroed” to that test standard. Optical testing equipment can measure positive or negative variations from the test standard when performing an O.D. test on a specific size oilfield tubular. A printout to an inspection operator can indicate the positive or negative variation of the tubular diameter compared to the test standard. Such a method has several problems. A relatively long time period is required to recalibrate the equipment each time a different size oilfield tubular is to be tested. Often it is preferable to test oilfield tubular diameter and ovality at the same time each tubular is being checked for material defects with non-destructive testing equipment, and the time required to recalibrate the optical equipment for checking a tubular diameter slows down the overall inspection process. Many inspection yards maintain a complete set of different oilfield tubular diameter test standards to be used to calibrate the optical inspection equipment, and these tubular diameter test standards must be carefully maintained, since any variation of the test standard will lead to incorrect diameter variation measurements.
In one prior art system and method oilfield tubular diameter and ovality are tested at a relatively high feed through tubular speed, and the test data is output to an inspection operator in real time, i.e., data for a specific tubular is available to the inspection operator while that tubular is being tested. This prior art diameter and ovality testing equipment can utilize optical techniques which recognize that the spacing between the “passing portion” of two light beams each striking the tubular in a direction traverse to the tubular axis is directly related to the diameter of the tubular at that test location; and light sensors thus detect the width of the light beam transmitted past the tubular. Signals from the sensors are input to a computer and then output to a screen and/or conventional data storage device to provide real-time diameter measurements. A tubular may be rotated as it is moved axially through the test equipment and the ovality test is obtained as a function of successive diameter measurements. This prior art equipment may be compatible with non-destructive testing equipment, so that a lot of tubulars may be tested for material defects and for diameter and ovality conformance at the same time. Such a system and method is described in U.S. Pat. No. 5,867,275 incorporated herein in its entirety for all purposes. In one aspect this prior art system has apparatus for testing the diameter of tubulars having various nominal diameters, including a machine frame for successively receiving axially moveable tubulars; first and second radially opposing carriages each moveable relatively to the machine frame such that an axially moveable tubular passes between the radially opposing carriages; first and second light generating sources mounted on their respective first and second carriages for transmitting respective first and second wide light beams directed to intersect radially opposing sides of the tubular spaced between the carriages, such that the width of the first and second light beams is reduced by engagement with the tubular and first and second reduced width light beams pass by the tubular; first and second light sensors each mounted on the carriages for detecting the respective first and second reduced width light beams while the tubular moves axially past the first and second light beams and generating test signals in response thereto; first and second optical shutters mounted on the carriages and each moveable with respect to the respective light beam from an active standardization check position to an inactive tubular-test position, each optical shutter having an opening therein for transmitting a pre-selected reduced width light beam past the shutter; and a computer for receiving the test signals from the first and second light sensors and generating a tubular diameter test measurement in response thereto.
In certain prior art systems pipe is inspected as it exits from pipe manufacturing apparatus. As it exits, it is not being rotated. If the manufacturing method is altered to rotate the pipe, pipe production rate is decreased.
There is a need, recognized by the present inventors, for an efficient and effective tubular inspection system which accurately measures tubular diameter. There is a need, recognized by the present inventors, for an efficient and cost-effective tubular inspection system that can accurately take into account the off-centering of a tubular during inspection. There is a need, recognized by the present inventors, for such systems that efficiently and accurately transmit and process signals related to tubular diameter measurement.